"lightweight" refers to two things(and will help you buy stuff in the future. And since you didn't buy it, you'll get some slack here)
1. The receiver pulls 100 watts off the wall
2. Its power is rated at 4ohm and 10% distortion
What those two, together, mean is it produces a usable 10-ish watts per channel. An AVR can't produce more than it chews off the wall. So, if the specs were "legit" and not complete BS...this would produce...as advertised, 700 watts total. 100 does not create 700.
But it isn't listed in the specs if the rating came from 1 channel at a time(likely)...and they just "tagged it" x7. And yes...all the AVR manufacturers do that. But, the spec of "how much it chews off the wall" is a good indicator to how much power it actually does produce.
In AVR under $500(based on MSRP...not "what you can get it for"), the typical "how is it this cheap?" falls straight on the power supply. Most $500 AVR pull less than 250 watts off the wall. There are exceptions.
When you increase price, especially nearing $1000, is when you start seeing AVR that are starting to pull upwards of 600 watts off the wall. Some AVR around $1000 will even pull as much as 1000 watts off the wall. Finally, the "big dollar ones" will pull as much as 1300 watts off the wall. The "big dog" Anthem and Integra models($3000-ish) pull as much as 1600 watts. No, that does not mean they pull that much "all the time". Just means when you turn it up...it can grab more off the wall.
Back to speakers. The reality is, most people don't realize how little power they actually need to fill the room with sound. That falls on(and is almost always my main criteria in picking speakers) their efficiency.
I'm going to guess the speakers that come with this system(maybe it was in the manual...didn't read speaker specifics...if there were any) are roughly 84db or under.
What that means is they need 1 watt to produce 84db(or less if less efficient). To double the sound(which is 3db), it takes double the power. Another 3db take ANOTHER double of power...
84db is 1
87 db is 2
90 db is 4
93 db is 8
96 db is 16
and so on.
Now, let's say I send you over to the BIC DV52clrs(or its bigger brother the 62clrs). Last I checked it is roughly 90db efficient and costs around $80. The 62 costs around $135.
90db is 1
93db is 2
96db is 4
The BIC speaker on 4 watts is the same loudness(I'm guessing) as your current center is on 16 watts.